Ammonia-Oxidizing Bacteria and Archaea in Groundwater Treatment and Drinking Water Distribution Systems

The ammonia-oxidizing prokaryote (AOP) community in three groundwater treatment plants and connected distribution systems was analyzed by quantitative real-time PCR and sequence analysis targeting the amoA gene of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Results demonstrated that AOB and AOA numbers increased during biological filtration of ammonia-rich anoxic groundwater, and AOP were responsible for ammonium removal during treatment. In one of the treatment trains at plant C, ammonia removal correlated significantly with AOA numbers but not with AOB numbers. Thus, AOA were responsible for ammonia removal in water treatment at one of the studied plants. Furthermore, an observed negative correlation between the dissolved organic carbon (DOC) concentration in the water and AOA numbers suggests that high DOC levels might reduce growth of AOA. AOP entered the distribution system in numbers ranging from 1.5 × 10³ to 6.5 × 10⁴ AOPs ml⁻¹. These numbers did not change during transport in the distribution system despite the absence of a disinfectant residual. Thus, inactive AOP biomass does not seem to be degraded by heterotrophic microorganisms in the distribution system. We conclude from our results that AOA can be commonly present in distribution systems and groundwater treatment, where they can be responsible for the removal of ammonia.Ammonia can be present in source water used for drinking water production or added to treated water with chlorine to form chloramines as a disinfectant. However, the presence of ammonia in drinking water is undesirable because nitrification might lead to toxic levels of nitrite (29) or adverse effects on water taste and odor (4) and might increase heterotrophic bacteria, including opportunistic pathogens (29). Two-thirds of the drinking water in The Netherlands is produced from groundwater. Most of the groundwater used for drinking water production is anoxic with relatively high concentrations of methane, iron, manganese, dissolved organic carbon (DOC), and ammonia. Treatment of anoxic groundwater aims at achieving biologically stable water, because drinking water in The Netherlands is distributed without a disinfectant residual. As a result, a highly efficient nitrification process during rapid medium filtration is required.Nitrification is the microbial oxidation of ammonia to nitrate and consists of two processes: the oxidation of ammonia to nitrite by ammonia-oxidizing prokaryotes (AOP) and the oxidation of nitrite to nitrate by nitrite-oxidizing bacteria (NOB). Recently it was shown that in addition to bacteria, archaea also are capable of ammonia oxidation (13). Since then, ammonia-oxidizing archaea (AOA) have been found in many different ecosystems, including wastewater treatment systems (10, 20, 24). However, it is currently unknown if AOA are present in drinking water treatment processes and distribution systems. Recent studies have focused on nitrification in drinking water treatment (16, 28). In those studies, AOB and NOB were enumerated by traditional most-probable-number (MPN) methods using selective liquid media. However, MPN methods are time-consuming and underestimate the numbers of AOP and NOB (3). Quantitative real-time PCR has been used to quantify AOB in drinking water (12) and might be a useful tool for quantifying AOB and AOA in drinking water.In our study, a real-time PCR method targeting the amoA gene of AOB or AOA was developed to quantify numbers of AOP in drinking water. This real-time PCR method was used together with a phylogenetic analysis of the amoA gene of AOB and AOA to do the following: (i) determine the treatment steps where AOP dominates in the groundwater treatment train of three drinking water production plants in The Netherlands, (ii) quantify the AOP entering the distribution system and determine the fate of AOP during transport in the distribution system, and (iii) elucidate the role of AOA in nitrification during drinking water treatment and in distribution systems.